Radio telephones are known in which a fixed helical antenna is provided to allow radio communication with a base station. The antenna may be contained totally within the housing of the radio telephone, such that no external antenna protrudes from said housing. Alternatively, part of the antenna may extend from the housing.
Recently, radio telephones of this type have taken two distinct forms. Some radio telephones communicate with an associated telephone, usually connected to the public switch telephone network (PSTN). Radio telephones of this type operate in a similar manner to conventional telephones, however they may be operated from a handset which does not require a cord connecting it to the remainder of the telephone base station. Telephones of this type are commonly referred to as "cordless" telephones and from a Network Operator's point of view, they are perceived as conventionally configured telephones.
In addition, radio telephones are provided which operate within cellular networks and the radio link from the telephone to a base station is part of the telecommunications network. Usually, the radio portion of the telecommunications network is established by a plurality of base stations and radio telephones of this type would communicate with whichever base station provided the strongest signal. Furthermore, switching between base stations may occur as the telephone moves over a geographical area. Radio telephones of this type are commonly referred to as "mobile" telephones, a term which is often used to distinguish them from the previously defined "cordless" telephones. As used herein, the term "radio telephone" is intended to relate to both the "mobile" and "cordless" type telephones previously defined, along with more conventional radio telephone type communicators, which are only arranged to communicate directly with similar devices, and non-cellular mobile telephones.
In order to improve communication, particularly in mobile telephones, it is common for a helical antenna to extend beyond the housing of a radio telephone and for a retractable whip antenna to be extended from said housing when improved communication is required. An antenna for a portable cellular telephone is disclosed in U.S. Pat. No. 4,868,576 and comprises a helical coil extending from an outer housing of the telephone. In addition, a half wavelength whip antenna may be extended from within the housing such that, when so extended, it is capacitively coupled to the helical coil.
A problem with this arrangement is that the mobile telephone itself must be arranged such as to accept the extendable whip antenna when pushed into its retracted position. Thus, in many situations where the whip antenna is never required, it must still be accommodated within the device, thereby adding unnecessarily to the complexity and expense of the overall telephone.
It is envisaged that in future mobile communications will become widespread and that as network facilities increase, it will be desirable to reduce the complexity and expense of radio telephones. Consequently, it would be undesirable in many environments to construct telephones with retractable whip antennas, particularly if the telephones are designed to operate under conditions in which such antennas would rarely be required.
Cordless telephones are known in which rugged telescopic aerials may be extended from a housing when the telephone is in operation. In these known cordless telephones, the telephone itself usually sits on a support base that, provides recharge power for batteries and it is unusual for the telephone to be carried by a user when not in use. Furthermore, in the majority of cordless environments, the range of telephones is clearly restricted.
In the future, it is likely that cordless telephones, like mobile telephones, will operate in accordance with digital transmission standards. This will allow the telephones to operate over wider ranges and, in addition, allow them to operate in more sophisticated operating environments, such that a single cordless telephone may be capable of operating from a plurality of base stations. Thus, although it is unlikely that cordless telephones will develop to be as complex as mobile telephones, the tendency is towards telephones of this type becoming more portable, therefore it is undesirable for them to provided with cumbersome antenna arrangements.
Mobile telephones are known in which an antenna is physically attached to the mobile telephone when required. The antenna itself is threaded and thereby engages within a tapped hole within the mobile telephone housing such that, once so engaged, an electrical connection is provided between the telephone duplexor and the aerial itself, effectively by-passing internal or external helical antennas. A problem with such arrangements is that the telephone housing itself must be configured so as to receive such an antenna, which generally results in each particular telephone type only co-operating with a particular antenna type. A further disadvantage is that effort is required on the part of the user to configure the telephone for operation with or without its extended antenna. Under these circumstances, it is common for the telephone to be used permanently without its antenna or for its antenna to be permanently in position. Consequently, an operator runs the risk of the telephone operating incorrectly, without the antenna in place, or, alternatively, the telephone may be unnecessarily cumbersome, with the antenna in position in situations where it is not actually required.
Arrangements are also known in which a telephone co-operates with an antenna without the antenna being brought into physical contact with the telephone itself. In cars and other vehicles, it is possible to provided an externally mounted antenna which is electrically connected to an internal antenna. The internal antenna effectively re-radiates the received signal. Thus, in these circumstances, there is no electrical or capacitive coupling between the re-radiating antenna and the internal antenna of the telephone. The external antenna, as far as the telephone is concerned, is effectively the re-radiating antenna that re-radiates electro-magnetic radiation to the telephone's antenna.
A problem with such an arrangement is that a user has no control over the relationship between the car mounted antenna and the telephone mounted antenna. Furthermore, being mounted to a car, the antenna is of little benefit in other situations, unless a plurality of antennas are assembled for operation at positions where an operator is usually required to make telephone calls. Under these circumstances, of course, the advantages of radio telephones is somewhat mitigated, in that conventional land based telephones could also be provided at these positions.